"In addition to the higher speed rating, the 8/1 and 16/2 dispensed with the compression changeover system. Apparently Lister's engineers figured that with a slightly lower compression ratio than the original starting ratio, the engine would start reliably and could run continuously at this ratio without the complication of changing compression ratios. The removable auxiliary chamber inserts and changeover valve were replaced with a simple plug. The compression ratio was fixed at 17.5:1. This was done without altering the volume of the combustion chamber, by shimming the cylinder at the base to produce .030" more clearance between the piston crown and head, leaving a little more air in the cylinder space at TDC. Thus, the cylinders, pistons and heads remained interchangeable between the older and newer engines."
Yup,
As you have discovered your proposed use of the COV is kinda backwards, it will lower your compression if screwed out but you wouldn't want to run the engine with it screwed in. It sure sounds as if your injection is advanced too far or squish is too tight and correcting either would be an economical alternative to a COV I think? A quick and easy check would be to crank it as if trying to start but leave the fuel lever up. If it still kicks back on the crank handle them compression is doing it, ifnot then early injection timing is doing it.
Yes a properly set up 8/1 cranks over easier than a 6/1 with the COV cranked in but the difference is hard to feel even if you have both side by side to compare.
Data taken from the technical manuals says that a COV equipped engine when set to start should have around 600 PSI of compression. When set to running position you should read around 450 PSI.
A properly set up 8/1 type without COV should be around 560 PSI
My personal experience is that a properly set up engine that is broken in will be close to those figures but I caution against using them as a guide to setting squish. A lot of things affect cranking compression readings besides squish. Valve recession being one, valve sealing being another along with condition of piston, rings and bore. How fast the engine is cranked, temperature and probably a few more that I have neglected to name.